Truck pivot joint bearing and method of lubricating

ABSTRACT

A bearing assembly is disclosed having a pair of bearing members movable relative to one another. A space is defined between the bearing members, and a relatively thin coating of a greaseless, self-lubricating material is applied to the surface of at least one of the bearing members. A grease lubricant is disposed in the space defined between the bearing members such that both the grease lubricant and the greaseless material act to substantially lower the friction-generated heat that is encountered during operation.

FIELD OF THE INVENTION

[0001] The present invention relates to bearing assemblies, and moreparticularly to bearing assemblies having two bearing members movablerelative to one another and methods of lubricating these assemblies.

BACKGROUND OF THE INVENTION

[0002] Various bearing assemblies and methods of lubricating theseassemblies can be found in many applications. Typical bearing assembliesinclude a pair of bearing members that are movable relative to oneanother. More specifically, a bearing or bushing is typically acylindrical shell, with or without a flange, installed in a structuralhousing in conjunction with a mating shaft, pin, or bolt. Bearingshaving pinned joints typically are used for cyclic and oscillatorymotion, such as used in landing gear joints, control surface hingepoints, and actuating linkages.

[0003] The advantages of bearings are numerous. Bearings are relativelyeconomical replacement elements which extend the useful life of majorstructural elements by providing protection from wear, corrosion,deformation, and other service-limiting or failure-initiating damage.The two basic considerations for successful service performance of abearing are strength and life. Strength is the capability of the bearingto resist deformation and structural failure under static load. The lifeof the bearing is determined by its ability to resist wear, fretting,galling, and seizure under cyclic or oscillating motion.

[0004]FIG. 1A shows a typical bearing structure assembly 100, whereingrease 106, such as Royal MS 11 manufactured by Royal Lubricants, Inc.of East Hanover, N.J., is applied between bearing assembly memberscomprising a bearing 101 and pin 103 to lubricate the members as theymove relative to one another. Specifically, the grease 106 is disposedbetween the inner surface 102 of the bearing 101 and the outer surface104 of the pin 103. While grease is suitable for many applications,extreme pressure and movement by the bearing assembly members may causethe grease to lose its lubricity, which may lead to overheating andeventual failure of the bearing assembly and surrounding structures.

[0005] One application where this may occur is on a landing gearapparatus of an aircraft, and more particularly on a truck pivot jointbearing assemblies for an aircraft landing gear. The bearing assembliesused in this type of application typically include a relatively thickcoating of grease between the moving surfaces of the bearing. This isacceptable for most circumstances because the dynamic bearing pressuresand sliding velocities of the moving surfaces are relatively low.However, rough landing conditions, such as runways with deep cracks,crevices, potholes, and/or uneven surfaces, can cause excessive use ofand wear on the truck pivot joint bearing assemblies from the rapidshocks and extreme oscillations these surface abnormalities transfer tothe bearing assemblies. In some cases, it has been discovered that theserough conditions create as much as ten (10) times more energy than isgenerated under normal conditions. This additional energy is absorbed asheat by the bearing assemblies, which accounts for the damage thatoccurs when using conventional bearing assemblies in these environments.As a result, the high temperatures generated in these conditions causethe grease packed between the moving surfaces of the bearing assembliesto melt away and thus lose its effective lubricity. This is shown inFIG. 1B, wherein the grease 106 is no longer occupying the entire spacebetween the opposing bearing members 101, 103, which allows the innersurface 102 of the bearing 101 to have intimate contact with the outersurface 104 of the pin 103.

[0006] As the grease loses lubricity and the surfaces 102, 104 of thebearing assembly 100 begin to directly move against each other, severedamage or failure of the bearing assembly components is likely. Toprevent failure of the bearing assembly, time-consuming maintenance mustbe performed more frequently, which further adds to the cost ofmaintaining the aircraft in addition to the lost profits while theaircraft is under maintenance or repairs. Thus, it is desirable toprovide a lubricant to bearing components that is more resistant todynamic bearing pressures and heat generation in extreme conditions.

[0007]FIG. 2A shows another type of conventional bearing assembly. Inparticular, the bearing assembly 110 includes a bearing 111 and a pin113 having opposing surfaces 112 and 114, respectively. A dry,greaseless coating material 116 is applied to a desired surface byspraying or coating the surface, such as the inner surface 114 of thebearing 111. The greaseless, self-lubricating material 116 occupies thespace between the opposing bearing surfaces 112, 114 such that thesurfaces are only separated by the greaseless material. One example of agreaseless self-lubricating material 116 is a polyester, thermosetting,resin-based material incorporating polytetrafluoroethylene or Teflon®particles, such as the material manufactured under the name KAron byKamatics Corporation of Bloomfield, Conn. This type of material isproclaimed as self-lubricating, meaning no external grease is requiredto lubricate the bearing assembly 110. Indeed, greaseless lubricantssuch as shown in FIG. 2 were designed to overcome the disadvantages ofgrease lubricants shown in FIG. 1, particularly in terms of loadcapacity and service life. Other types of greaseless lubricants aredescribed in U.S. Pat. Nos. 3,929,396 and 3,996,143.

[0008] In particular, greaseless, self-lubricating materials operate atlower friction levels, which reduces the heat generated duringoperation. If heat does build up, the polytetrafluoroethylene particlestypically expand more rapidly than the underlying surfaces to fill thespace between the bearing surfaces, so that frictional contact betweenbearing surfaces 112, 114 is thwarted or delayed, at least temporarily.Conventional practice teaches that a thicker coating of the greaselessmaterial 116 will provide more lubrication for the bearing 110. Whiletrue for most applications, the extreme loading conditions mentionedabove may cause the greaseless material to break down. And because thegreaseless material 116 allows the bearing surfaces 112, 114 to beessentially in contact with each other separated only by the greaselesslubricant, any reduction in the thickness of the greaseless lubricantcan reopen the space between the bearing surfaces, which can damage thebearing or cause the bearing to fail. This is shown in FIG. 2A, whereinthe greaseless material 116 has worn down in certain areas, which allowsunwanted and damaging rattling or movement between the bearing assemblymembers 111, 113. Thus, while greaseless lubricants provide advantageousqualities over grease lubricants, there is a need to provide a bearingassembly having a lubricant that offers even better wear and heatresistance, which leads to longer operational life of the bearing. Thereis also a need to provide a bearing assembly having a lubricant that isresistant to extreme loading conditions, such that the lubricantprovides longer protection to the bearing in these environments comparedto protection from conventional lubricants before service is required.

SUMMARY OF THE INVENTION

[0009] These and other needs are provided, according to the presentinvention, by a bearing assembly that combines the benefits ofgreaseless lubricant materials and traditional grease lubricants toprovide longer bearing lubrication and protection compared toconventional bearings and methods of lubricating the bearings. Thebearing assembly of the present invention has been shown to provide upto 600% longer life than conventional grease-lubricated bearings undercertain operating conditions, which greatly reduces the maintenance costand frequency of the bearing.

[0010] In particular, the bearing assembly of the present inventioncomprises a pair of bearing members that are movable relative to oneanother. The members are typically metal, although other materials mayalso be used. In one embodiment, at least one of the members is formedof an aluminum, nickel, and bronze alloy, which is preferable because ithas shown to be very durable and highly resistant to wear. In addition,the members are spaced a slight distance apart to define a spacetherebetween, such as between 0.006-0.008 inch. At least one of thebearing members has a bearing surface having a relatively thin coatingof a self-lubricating, greaseless, polytetrafluoroethylene-basedmaterial thereupon. The coating, which according to one embodiment isabout 0.003-0.007 inch, can be applied one of many ways, includingspraying, coating, or dipping.

[0011] The thin coating of greaseless material does not occupy theentire space between the pair of bearing members. The remaining space isinstead occupied by a grease lubricant. Accordingly, the greaselubricant and the greaseless lubricant act in conjunction with oneanother to lubricate the bearing members. Advantageously, it has beendiscovered that, despite the teachings that greaseless lubricantmaterials are not to be used in conjunction with grease lubricants, adramatic improvement in bearing and lubrication life is realized bycombining a relatively thin layer or coating of greaseless lubricantwith a grease lubricant in the space defined by the bearing members.

[0012] The bearing assembly of the present invention is particularlyadvantageous for use in extreme conditions, such as where the bearingassembly is subjected to great dynamic pressures and oscillations. Forexample, truck pivot joint bearing assemblies used in aircraft landinggear are prime candidates for employing the teachings of the bearingassembly of the present invention, as truck pivot joint bearingassemblies may encounter great dynamic pressures and oscillations duringlanding cycles. Of course, the bearing assembly of the present inventioncan also be used in many other applications where the loading conditionsare not extreme, as the longer lubrication and bearing life isappreciable in a broad range of applications.

[0013] Thus, the present invention provides a bearing assembly having animproved bearing life and requiring less frequent maintenance cycles tothe bearing components. By combining the thin layer of greaselessmaterial with a grease lubricant in the space defined between the twobearing members, at least two advantages are realized. First, the thinlayer or coating of greaseless material provides a lower coefficient offriction compared to grease lubricants, which delays the onset of heatbuildup and loss of lubricity. Second, the grease lubricant provides aless-rigid material for moving about and occupying the space between thebearing members, which further improves bearing life.

[0014] By contrast, using only a greaseless coating (i.e., a relativelythick coating as taught by conventional bearings) between the bearingmembers can result in unwanted play between the surfaces of the bearingassembly as the coating wears away. By using a relatively thingreaseless coating in conjunction with a grease lubricant, thegreaseless lubricant receives little or no contact with the opposingbearing surface and thus wears more slowly. In addition, the greaselubricant fills the space between the bearing assembly surfaces toprevent unwanted movement or play. And because the thin greaselesscoating reduces the friction and heat generated during loading cycles,the grease lubricant's life span is increased. Thus, the bearingassembly of the present invention provides a clear advantage overconventional bearing assemblies and lubrication techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Having thus described the invention in general terms, referencewill now be made to the accompanying drawings, which are not necessarilydrawn to scale, and wherein:

[0016]FIGS. 1A and 1B are cross-sectional views of a bearing assemblyaccording to the prior art;

[0017]FIGS. 2A and 2B are cross-sectional views of a bearing assemblyaccording to the prior art;

[0018]FIG. 3 is a side view of a landing gear assembly for an aircraftaccording to one embodiment of the present invention;

[0019]FIG. 4 is a cross-sectional view of a truck pivot joint bearing ofthe landing gear assembly as viewed along line 4-4 of FIG. 3;

[0020]FIG. 5 is a side perspective view of a truck pivot bushingaccording to one embodiment of the present invention;

[0021]FIG. 6 is a cross-sectional view of a truck assembly according toone embodiment of the present invention; and

[0022]FIG. 7 is a cross-sectional view of a bearing assembly as viewedalong line 7-7 of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention now will be described more fullyhereinafter with reference to the accompanying drawings, in whichpreferred embodiments of the invention are shown. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. Like numbers refer to like elements throughout.

[0024] FIGS. 3-6 show various views of portions of a landing gearassembly 10 for an aircraft, such as a Boeing 757. The landing gearassembly 10 includes at least one shock strut 12 that is rotatablyconnected to a truck pivot pin 24. Specifically, the shock strut 12defines an opening for rotatably receiving the truck pivot pin 24. Theshock strut 12 also includes a distal portion called an inner cylinderfork 26 that extends away from the opening. The landing gear assembly 10also includes a truck pivot bearing assembly, shown generally as 20. Thebearing assembly 20 includes a truck assembly 14 that is rotatablyconnected to the truck pivot pin 24, and at least two pairs of wheels 16are attached to the truck assembly 14.

[0025]FIGS. 4 and 6 show cross sectional views of the bearing 20,wherein FIG. 6 is a cross sectional view of the truck assembly 14forming part of the bearing 20 shown in FIG. 4. As shown in FIG. 6, thetruck assembly 14 defines a cavity 34 therethrough having an innersurface 31. The truck assembly 14 is preferably formed of metal, such asa high strength steel alloy, although other metals or materials may alsobe used, such as titanium. The truck pivot pin 24, which in oneembodiment is a chrome plated pin, extends through the cavity 34 of thetruck assembly 14. A pair of truck pivot bushings 30 are positioned atopposing ends of the truck assembly 14 such that flanged surfaces 33 ofthe pivot bushings engage sidewalls 23 of the truck assembly. Inaddition, a pair of back-to-back inner cylinder pivot bushings 40 arepositioned proximate the inner cylinder forks 26 such that the innercylinder assemblies are separated from the truck assembly 14 by thepivot bushing 30 and the inner cylinder pivot bushings 40. In thisregard, the truck pivot bushings 30 and inner cylinder pivot bushings 40provide low-friction support to the truck pivot pin 24 as it rotatesinside the truck assembly 14 and shock struts 12. A splined washer 28helps secure the inner cylinder pivot bushings 40 about the pivot pin24, and multiple pairs of brake rods 42 extend substantially parallel tothe truck assembly 14.

[0026] As shown in FIG. 4, the pivot bushings 30 are interposed betweenthe truck assembly 14 and the truck pivot pin 24. As shown in FIG. 5,each pivot bushing 30 is generally tubular, and preferably defines aplurality of lubrication distribution grooves 36 that receive anddistribute grease between the truck pivot pin 24 and the pivot bushings30 so that the pivot pin 24 is rotatable relative to the truck assembly14. Each pivot bushing 30 also includes an outer surface 32 that ispositioned proximate the inner surface 31 of the truck assembly 14 in apress-fit or interference fit so that the pivot bushing 30 does not moverelative to the truck assembly 14. A seal 38 is disposed proximate thelubrication distribution grooves 36 such that grease or other lubricantis prevented from escaping. According to one embodiment, the seal 38 isformed from an elastomer, although other materials could also be used toform the seal. As shown, each pivot bushing 30 engages a sidewall 23 ofthe truck assembly 14 and an adjacent inner cylinder pivot bushing 40 tofurther seal the pivot bushing and the truck assembly 14.

[0027]FIG. 7 shows a detailed cross-sectional view of the truck assembly14, pivot bushing 30, and pivot pin 24 according to a preferredembodiment of the present invention. In particular, the pivot bushing 30is disposed radially inwardly of the truck assembly 14 and is securedthereto by a frictional interference fit. The inner surface 35 of thepivot bushing 30 is proximate the pivot pin 24, and an advantageouslubricant according to the present invention is interposed therebetween.According to one embodiment, the inner surface 35 of the pivot bushing30 is coated with a greaseless, self-lubricating material 50. It is alsopossible to apply the relatively thin coating of greaseless material 50on both the inner surface 35 of the pivot bushing 30 and the outersurface of the pivot pin 24. Alternatively, only the outer surface ofthe pivot pin 24 may be coated with the greaseless material 50, althoughpreferably only the inner surface 35 of the pivot bushing 30 includesthe greaseless material 50. The material 50 is preferably apolytetrafluoroethylene-based material, such as a material sold underthe trade name KARON by Kamatics Corporation of Bloomfield, Conn. Thegreaseless material 50 can be applied to the inner surface 35 of thepivot bushing 30 in a number of ways, such as spraying, brushing on, orby dipping the pivot bushing 30 in a bath of the greaseless material.The greaseless material 50 includes a solid particulate, such asTeflon®, that is embedded in a stabilizer material in the form offlocked, powdered, fibrous, flaked, beaded, or other forms. Otherparticulate materials may also be used, such as silver powder, leadpowder, and the like. The greaseless material 50 has a thickness ofabout 0.003-0.007 inch, and preferably about 0.005 inch. As shown inFIG. 7, the thickness of the greaseless material 50 is not enough tosubstantially fill the space defined by the pivot bushing 30 and thepivot pin 24.

[0028] Advantageously, the space defined by the pivot bushing 30 and thepivot pin 24 not occupied by the greaseless material 50 is occupied orfilled by a grease lubricant 58, such as an extreme pressure grease soldunder the name Royco 11MS manufactured by Royal Lubricants, Inc. of EastHanover, N.J. Other types of greases may also be used, such as anyextreme pressure grease that is apparent to one of skill in the art. Thechosen grease must be highly resistant to extreme dynamic bearingpressures and temperatures.

[0029] The combination of a relatively thin coating of the greaselessmaterial 50 coupled with the grease lubricant 58 as disclosed by thepresent invention flies in the face of conventional lubrication systemsand methods. In this regard, it has been discovered that applying arelatively thin coating, such as about 0.005 inch, of the greaselessmaterial 50 in combination with the grease lubricant that fills theremainder of the gap between the pivot bushing 30 and the pivot pin 24allows dynamic bearing pressures to be increased dramatically to a levelthat approaches the allowable pressures for the base bearing material.More particularly, the relatively thin layer or coating of greaselessmaterial 50 has a friction coefficient of only about 0.08, whereasgrease lubricants have a friction coefficient of about 0.20. Asdiscussed above, conventional applications of greaseless materialcoatings call for much thicker coatings, which has been discovered tolimit their use at relatively low dynamic bearing pressures and slidingvelocities. Accordingly, the bearing assembly 20 according to thepresent invention can operate longer under extreme conditions, such aswhen landing aircraft on very rough runways where the bearing receivessevere oscillations and sliding velocities. Specifically, the bearingassembly 20 according to the present invention reduces thefriction-generated heat sufficiently to substantially reduce oreliminate damage to the truck assembly 14 or inner cylinder assembly 26.

[0030] Another advantage of the bearing assembly 20 according to thepresent invention is that the combination of greaseless,self-lubricating material 50 and the grease lubricant 58 can be appliedin existing bearing assemblies, such as those found in aircraft landinggear assemblies, without having to redesign the assemblies to handle theextreme conditions. Thus, existing aircraft landing gear can easily beretrofitted with the bearing assembly 20 of the present invention, whichis significantly less expensive than redesigning a new type of landinggear assembly or bearing configuration. In addition, the bearingassembly 20 of the present invention requires less frequent maintenancecompared to conventional bearings operating under similar conditions,which substantially reduces maintenance man hours, downtime, and overalloperating costs. In fact, it has been discovered that up to a 600%improvement in life span is achieved in comparison to conventionalgrease-lubricated bearings by applying the bearing assembly 20 of thepresent invention to truck pivot joint bearings in large jet aircraftlanding gear assemblies.

[0031] Many modifications and other embodiments of the invention willcome to mind to one skilled in the art to which this invention pertainshaving the benefit of the teachings presented in the foregoingdescriptions and the associated drawings. Therefore, it is to beunderstood that the invention is not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims. Forexample, the teachings of the present invention, namely a bearingassembly 20 having the relatively thin coating 50 of greaseless,self-lubricating material in combination with a grease lubricant 58 usedin combination in the space defined between the inner and outer membersof a bearing assembly, can be applied to many industries in addition tothe aerospace industry where lower friction bearings are desired. Inaddition, the teachings of the present invention regarding thecombination of a greaseless, self-lubricating material used incombination with a grease lubricant could be applied to a broad range ofapplications, including applying the combination to a nut and boltcombination, or similar applications. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

That which is claimed:
 1. A bearing assembly, comprising: a pair ofbearing members movable relative to one another, said pair including afirst member and a second member that define a space therebetween, atleast said first member having a bearing surface having a relativelythin coating of a polytetrafluoroethylene-based material thereupon; anda grease lubricant occupying the space defined between the first memberand the second member, wherein the polytetrafluoroethylene-basedmaterial and the grease lubricant act in conjunction with one another tolubricate the first and second members.
 2. A bearing assembly accordingto claim 1, wherein the coating is a polytetrafluoroethylene-basedmaterial having a solid particulate in a form selected from the groupconsisting of flocked, powdered, fibrous, flaked, beaded, andcombinations thereof.
 3. A bearing assembly according to claim 1,wherein the coating has a thickness of about 0.003-0.007 inch.
 4. Abearing assembly according to claim 1, wherein the first member isformed from the group consisting of steel, titanium, aluminum, nickel,bronze, and alloys thereof.
 5. A bearing assembly according to claim 1,further comprising a seal positioned in the space defined between thefirst member and the second member.
 6. A bearing assembly according toclaim 1, wherein the coating is a self-lubricating material.
 7. Abearing assembly for a truck pivot joint bearing in an aircraft landinggear, the assembly comprising: a metallic truck assembly defining anopening therein; a pin rotatably positioned in the opening of the truckassembly; a truck pivot bushing positioned at least partially in theopening defined by the truck assembly, the truck pivot bushing having aninner surface proximate said pin such that a space is defined betweenthe inner surface of the truck pivot bushing and the pin, at least aportion of the inner surface of the truck pivot bushing having arelatively thin coating of a self-lubricating, greaseless material; anda grease lubricant occupying the space defined between the pivot bushingand the pin.
 8. A bearing assembly according to claim 7, wherein thecoating is a polytetrafluoroethylene-based material.
 9. A bearingassembly according to claim 8, wherein the coating has a solidparticulate in a form selected from the group consisting of flocked,powdered, fibrous, flaked, beaded, and combinations thereof.
 10. Abearing assembly according to claim 7, wherein the coating has athickness of about 0.003-0.007 inch.
 11. A bearing assembly according toclaim 7, wherein the pivot bushing is formed from the group consistingof steel, titanium, aluminum, nickel, bronze, and alloys thereof.
 12. Abearing assembly according to claim 7, further comprising a sealpositioned in the space defined between the truck assembly and the pin.13. A method of manufacturing a bearing assembly having a pair ofbearing members movable relative to one another, the method comprising:applying a relatively thin coating of a self-lubricating, greaselessmaterial on a portion of a first member of the pair of bearing members;positioning a second member of the pair of bearing members proximate thefirst member to define a space therebetween; and introducing a greaselubricant between the first member and the second member such that thegrease lubricant substantially occupies the space defined therebetween.14. A method according to claim 13, wherein the grease lubricantintroducing step includes introducing an extreme pressure grease.
 15. Amethod according to claim 13, wherein the applying step includes coatingthe first member with a polytetrafluoroethylene-based material.
 16. Amethod according to claim 13, further comprising removing the bearingassembly from an aircraft landing gear before said applying step,whereby the greaseless material and the grease lubricant are retrofittedin existing aircraft landing gear.
 17. A method of lubricating a bearingassembly having a pair of bearing members movable relative to oneanother, the method comprising: positioning the pair of bearing membersproximate each other to define a space therebetween; applying a coatingof a polytetrafluoroethylene-based, greaseless material to at least aportion of one of the members of the pair of members; and introducing agrease lubricant so as to occupy the space defined between the members,wherein the grease lubricant is in contact with the coating ofgreaseless material.
 18. A method according to claim 17, furthercomprising removing the bearing assembly from an aircraft landing gearbefore said applying step, whereby the greaseless material and thegrease lubricant are retrofitted in existing aircraft landing gear.